The present invention is related to an auxiliary equipment of driving force to be installed in a drive system of an electrically power augmented bicycle which has an electric motor and is capable of reducing pedaling forces for the pedals of the bicycle whereby the number of revolutions of a rotatable shaft of the electric motor is reduced before transmitting to the pedal shaft.
Recently becoming popular is an electrically power augmented bicycle which utilizes the power of an electric motor to reduce the pedaling forces of the rider to the pedals of the bicycle, so that even the rider with weak power can ride up along the slope, and that the fatigue of the rider is reduced.
The structure of the electrically power augmented bicycle is disclosed for example in Japanese Patent First Publication Toku Kai Hei7-95744. In the electrically power augmented bicycle as described in this publication, as shown in FIG. 1, a pedal shaft 3 is rotatingly driven through a pair of cranks 2 by pedaling a pair of pedals 1 (see FIG. 2) of the bicycle (not shown) to produce a torque. In the auxiliary equipment of driving force for bicycling installed in the bicycle, a driving force is added to the pedal shaft 3, such that the driving force has a magnitude corresponding to the torque applied through the pedals 1 and is added to the torque through the pedals 1.
The auxiliary equipment of driving force for bicycle comprises a battery (not illustrated), an electric motor 5 (see FIGS. 2, 3 and 6) to rotate its rotatable shaft 4 in a predetermined direction based on the electric power from the battery, and a reduction gear apparatus 31 provided between the rotatable shaft 4 of the motor 5 and the pedal shaft 3. The reduction gear apparatus 31 contains a planetary roller type reduction gear 32.
The reason for using the reduction gear apparatus 31 containing the planetary roller type reduction gear 32 for the auxiliary equipment of driving force is as follows;
In order to secure the efficiency of the motor 5 and to prolong the life of the battery so as to make the traveling length long, the motor 5 must be rotated at a high speed. The term xe2x80x9ctraveling lengthxe2x80x9d means the xe2x80x9ctraveling length with an auxiliary power usedxe2x80x9d throughout the present specification.
On the other hand, the driving force for rotation must be applied to the pedal shaft 3 at a relatively low speed and with a large torque. Therefore, the reduction gear apparatus 31 is provided between the electric motor 5 and the pedal shaft 3 to reduce the rotating speed of the rotatable shaft 4 of the motor 5 and to increase the torque for transmission of the torque to the pedal shaft 3.
The reduction gear of the planetary roller type 32 is placed at the first stage of the reduction gear apparatus 31 to prevent uncomfortable noise from being produced from the reduction gear apparatus 31.
Specifically, the speed reduction apparatus using xe2x80x9cgearsxe2x80x9d such as the planetary gear type has a good transmission efficiency but produces jarring high frequency noise during high speed operation. Accordingly, the first stage in the, reduction gear apparatus having the highest operation speed is desirably provided with the reduction gear of the planetary roller type 32 with low noise so that the noise produced during the operation of the reduction gear apparatus 31 is reduced
Incidentally, the auxiliary equipment of driving force for bicycle described in Japanese Patent First Publication Toku Kai Hei7-95744 is provided with a reduction gear of the planetary roller type 32 at the first stage, with a reduction gear of the bevel gear type 33 at the intermediate stage, and with a reduction gear of the planetary gear type 34 at the final stage. Disposed between the reduction gear of the planetary roller type 32 and the bevel gear type reduction gear 33 is a one way clutch 35 such as roller clutch which can afford to transmit the rotation force only to the pedal shaft 3 from the motor 5. The one way clutch 35 is utilized to separate the pedal shaft 3 from the rotatable shaft 4 of the motor 5 to prevent the existence of the motor from being a resistance against the running in the state of running without pedaling such as inertia moving, downward riding.
The reduction gear of the planetary roller type 32 having the auxiliary equipment of driving force for bicycle as described in Japanese Patent First Publication Toku Kai Hei7-95744 comprises a housing 36 fixed so as to cover the end of the rotatable shaft 4 of the motor 5, four support shafts 37 provided in parallel with the rotatable shaft 4 around the rotatable shaft 4 within the housing 36, four planet rollers 38 rotatably supported by the support shafts 37, and an outer ring 39 having a cylindrical inner surface and fixed to a portion surrounding the planet rollers 38 within the housing 36. Disposed to support the support shafts 37 is a connecting member 40 which can function as an output shaft of the reduction gear of the planetary roller type 32, so that the spinning action of the planet rollers 38 can be taken out as a rotating output of the reduction gear of the planetary roller type 32.
The outer peripheral surfaces of the planet rollers 38 are abutted to the outer peripheral surface of the rotatable shaft 4 of the motor 5 and the inner peripheral surface of the outer ring 39.
In the case of the auxiliary equipment of driving force for bicycle as disclosed in Japanese Patent First Publication Toku Kai Hei7-95744, it is hard to make high the efficiency of transmission of the reduction gear of the planetary roller type 32 in the whole range, which is a bar in making long the traveling distance of the electrically power augmented bicycle.
This Reason is as Follows:
The outer peripheral surfaces of the planet rollers 38 must not slip on the outer peripheral surface of the rotatable shaft 4 of the motor 5 and on the inner peripheral surface of the outer ring 39 at the contact portions to secure the efficiency of transmission of the reduction gear of the planetary roller type 32. In addition, the contact pressure between the pairs of the peripheral surfaces at the contact portions must be made large to avoid the slip at the contact portions. Accordingly, in the reduction gear of the planetary roller type 32 installed in the conventional auxiliary equipment of driving force for bicycle, the planet rollers 38 are provided under pressure in interference fitting between the outer peripheral surface of the rotatable shaft 4 of the motor 5 and the inner peripheral surface of the outer ring 39 to secure the contact pressure at the contact portions.
Provided that the contact pressure is constant, as the torque transmitted through the reduction gear of the planetary roller type 32 is larger, the surface portions at the contact portions are easier to slip. Accordingly, conventionally, the contact pressure is controlled to be large, so that the surface portions at the contact portions do not slip with reference to each other even in the state where the torque transmitted through the reduction gear of the planetary roller type 32 is at a maximum as in riding upward along the steep slope. However, when the contact pressure is larger between the peripheral surfaces in rolling contact, the rolling resistance is larger, so that the power loss in the reduction gear of the planetary roller type 33Z is larger.
Specifically, in the state such as in riding along a flat land at a constant speed where the torque transmitted through the reduction gear of the planetary roller type 32 is small and there is no possibility of relative slip between the surface portions at the contact portions even with a low contact pressure, an excessive contact pressure is applied to the contact portions, so that the loss inside the reduction gear of the planetary roller type 32 is larger. Consequently, the transmission efficiency is low at the constant speed along the flat land, which is the most typical traveling style, so that the battery to supply power to the motor 5 is outstandingly exhausted. As a result, it is hard to prolong the traveling distance of the electrically power augmented bicycle.
An objective of the present invention is to provide an auxiliary equipment of driving force for bicycle wherein a reduction gear of the traction roller type having a structure different from the reduction gear of the planetary roller type is adopted taking into consideration the circumstances above, where the contact pressure between the outer peripheral surfaces of the traction rollers and the outer peripheral surface of the rotatable shaft and the inner peripheral surface of the outer ring is controlled corresponding to the torque to be transmitted, so that the battery is less exhausted and that the traveling distance of the electrically power augmented bicycle is prolonged.